Smith, 32, is 40-27 with a 2.94 ERA (182 ER/556.1 IP) in 623 major league relief appearances covering the last 10 seasons with the New York Mets (2007-08), Cleveland Indians (2009-13) and Los Angeles Angels (2014-16). He has reached 70 relief outings in each of the last five seasons and has pitched in both closing and set-up situations the last three years, totaling 26 saves and 56 holds since the start of the 2014 campaign.

In his career, Smith has limited foes to a .226 batting average and .306 on-base percentage while allowing only 0.60 home runs per nine innings, contributing to a .326 career slugging percentage against. He has limited right-handed hitters to a career .214 batting average against.

Smith is 1-4 with six holds, six saves and a 3.82 ERA (16 ER/37.2 IP) in 38 relief appearances with the Angels this season. In his last 17 outings in the last two-plus months starting on May 23, he has pitched to a 2.87 ERA (5 ER/15.2 IP).

Castillo, 20, is 2-3 with a 3.27 ERA (12 ER/33.0 IP) in seven starts for Single-A Eugene this season. He was originally acquired by the Cubs as part of the trade that sent outfielder Tony Campana to the Arizona Diamondbacks on February 18, 2013.